FIG. 12 is a circuit block diagram of a first related art example of a light emitting diode (LED) driving device. The LED driving device of the first related art example is configured to control an output feedback of a switching regulator (which is a power circuit for generating an output voltage Vo applied to anodes of an array of LEDs from an input voltage Vi) based on a feedback voltage Vfb extracted from cathodes of the array of LEDs. Simultaneously, the conventional LED driving device executes dimming of the array of LEDs by pulse width modulation (PWM)-controlling a driving current ILED (LED current) flowing through the array of LEDs.
In the LED driving device of the first related art example, when an ON period Ton of a dimming signal PWM is longer than a driving period Tsw of a switch signal SW, the ON period of the switch signal SW can be sufficiently secured without causing shortage of an inductor current IL, and an output voltage Vo can be maintained at a target value (see FIG. 13).
However, when the ON period Ton of the dimming signal PWM is shorter than the driving period Tsw of the switch signal SW, the ON period of the switch signal SW cannot be sufficiently secured and the inductor current IL is insufficient to lower the output voltage Vo from the target value, failing to allow the driving current ILED to flow to the array of LEDs (see FIG. 14).
FIG. 15 is a circuit block diagram of a second related art example of an LED driving device. The LED driving device of the second related art example is configured to control output feedback of a switching regulator based on a feedback voltage Vfb obtained by dividing an output voltage Vo. Simultaneously, the LED driving device executes dimming of an array of LEDs by PWM-controlling a driving current ILED flowing through the array of LEDs. In this manner, when controlling the output feedback of the switching regulator is completely independent from controlling the dimming of the array of LEDs, the output voltage Vo can be maintained at a target value, without having to follow an ON period Ton of a dimming signal PWM. However, in the LED driving device of the second related art example, unlike that of the first related art example, since the target value of the output voltage Vo is set to be high in consideration of the fact that a forward dropped voltage VF of the array of LEDs is not even, power conversion efficiency is poor.
Meanwhile, the technical problem of the related art has been described by using a LED driving device as an example, but other load driving devices (e.g., a power circuit for supplying power to a pulse-driven load or the like) also have the same problem.